Explanation:
Big, beautiful spiral galaxy M101 is one of the last
entries in Charles Messier's
famous catalog, but definitely not
one of the least.
About 170,000 light-years across,
this galaxy is enormous, almost
twice the size of our own Milky Way Galaxy.
M101 was also one of the original
spiral
nebulae
observed by Lord Rosse's large 19th century telescope, the
Leviathan
of Parsontown.
Recorded at
infrared wavelengths
by the Spitzer Space telescope, this
21st century view
shows starlight in blue hues while the galaxy's
dust clouds are in red.
Examining the dust features in the outer rim of the
galaxy,
astronomers
have found that organic molecules present throughout
the rest of M101 are lacking.
The organic molecules tracked by Spitzer's instruments are
called polycyclic aromatic hydrocarbons
(PAHs).
Of course, PAHs are common components of dust in the
Milky Way
and on planet Earth are found in soot.
PAHs are likely destroyed near the outer edges of M101 by energetic
radiation in intense star forming regions.
Also known as the
Pinwheel Galaxy,
M101 lies within the boundaries of the northern constellation
Ursa Major, about 25 million light-years away.